Researchers pursue anaplasmosis vaccine

Molecular biologist Susan Noh, at the Agricultural Research Service’s Animal Disease Research Unit in Pullman, Washington, is working to develop a vaccine to protect against anaplasmosis, a tick-transmitted disease of cattle. Caused by the microbe Anaplasma marginale, anaplasmosis affects cattle health, well-being, and production in many parts of the world and is characterized by severe anemia, fever, and weight loss. Despite this threat, there is no widely accepted vaccine for anaplasmosis.

Through their studies, Noh and her colleagues at Washington State University have identified important proteins to include in a potential vaccine, which is now being tested on animals. They found that small groups of the outer surface proteins of A. marginale induce an immune response that not only reduces symptoms, but can also prevent A. marginale infection in some animals. Some of the more promising vaccines being tested have protected 80 to 90 percent of the animals from clinical disease and have prevented infection in up to 40 percent of the animals.

“This is significant because infected animals may have no clinical evidence of infection, yet serve as sources of infection for others,” says Noh. “No vaccine has ever prevented infection from A. marginale in cattle.” Other countries have used an attenuated (weakened) strain (usually A. centrale) as a vaccine, and that vaccine protects against clinical disease, but not infection. Attenuated vaccines are prepared from live microorganisms or viruses that are cultured in the lab in such a way that they lose their virulence, but still confer disease immunity.

“To date we have only tested the vaccine against one strain of Anaplasma. In the field, many strains coexist. The next step is to determine whether this particular group of surface proteins will protect cattle from multiple strains of Anaplasma,” says Noh.